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Lalit Mishra, Nitin Meena / International Journal of Engineering Research and Applications
(IJERA)
ISSN: 2248-9622
www.ijera.com
Vol. 3, Issue 4, Jul-Aug 2013, pp. 462-465
A Novel Approach to Design a High Performance Domino Cmos
Logic
Lalit Mishra1, Nitin Meena Assistant Professor2
1
Department of VlSI and Embedded System
Department of VLSI and Embedded System IES College of Technology, RGTU ,Bhopal
2
Abstract
In this paper a Domino Cmos logic
circuit is design with aim to reduction in power
consumption, time delay and energy efficient.
Due to rapid growth in VLSI Technology, an
integrated circuit has demand with low power,
high performance, compatible, small in size and
easy to recodify. Dynamic
cmos gates are
inherently less resistance to noise than static
cmosgate. Sothis approach allow low power ,
noise tolerant and high performance. Domino
cmos logic is a form of dynamic logic that gives
output in cascaded form and it consume higher
dynamic switching speed, leakage power and
weaker noise immunity.This design has
Simulated and analyzed on 0.12 Microwind2
tool technology .
Keyword – Domino Logic, Dynamic
circuit,Delay, Low Power ,Noise Tolerant,
I.
Introduction
Due to continuously increasing chips
complexity and number of transistors, circuit’s
power consumption is growing . Technology trends
shows that circuit delay is scaling down by 30%,
performance and transistor density are doubled
approximately every two years, and the transistor’s
threshold voltage is reduced by almost 15% every
generation. These entire technology trend leads to
higher and higher power in circuits .Domino logic is
a CMOS-based evolution of the dynamic logic
techniques which were based on either PMOS or
NMOS transistors. It allows a rail-to-rail logic
swing. It was developed to speed up circuits.Domino
CMOS logic circuit family finds a wide variety of
applications in microprocessors, digital signal
processors, and dynamic memory due to their high
speed and low device count. However, for wide fan
in domino logic, that is when there is a long chain of
NMOS transistors.(6)
II.
Review of Domino logic circuit
The basic dynamic domino logic gate is
shown in Fig 1. As shown in the figure, it consists of
a pull-down network (PDN) that realizes the desired
logic function and there are two switches in series
that are periodically operated by the clock signal,
CLK. CL denotes the total parasitic capacitance
between the dynamic node and ground. When CLK
is low, QP is turned on, and the circuit is in the
precharge phase where the dynamic node charges to
VDD.
Also, during precharge, the inputs are
allowed to change and settle to their proper values.
Because Qeis off, no path to ground exists. When
CLK is high, QP is off and Qeturns on, and the
circuit is in the evaluation phase.
Fig.1. Circuit of domino logic circuit
During the evaluation phase; there are two
possibilities for the dynamic-node voltage. If the
input combination is one that corresponds to a low
output, the dynamic-node voltage must be
maintained at the supply voltage, VDD. On the other
hand, if the input combination is one that
corresponds to a high output, the dynamic-node
capacitor, CL must be discharged to ground through
the conducting NMOS transistors of the PDN. The
inverter at the output node is put for allowing this
stage to be cascaded with another one. Specifically,
if the dynamic node of this stage is connected
directly to the gate of an NMOS transistor in the
PDN of the next stage and is at logic “1”, then this
transistor will conduct during the time interval from
the time of application of this “1” to the time at
which the dynamic-node capacitor, CL discharges
below the threshold voltage of this transistor. This
causes the dynamic-node capacitor of the second
stage to discharge as it mustn’t be. The conventional
problem that arises during the evaluation phase is
that the leakage current through the PDN of CL.
Also, the charge of CL may be shared with any of
the internal capacitors associated with the NMOS
transistors of the PDN. So, a PMOS keeper must be
used to replenish the lost charge as show in Fig.2.
This keeper must be week so that its current during
the evaluation phase is relatively small so that the
discharging of CL will not be slowed down.
462 | P a g e
Lalit Mishra, Nitin Meena / International Journal of Engineering Research and Applications
(IJERA)
ISSN: 2248-9622
www.ijera.com
Vol. 3, Issue 4, Jul-Aug 2013, pp. 462-465
Fig.2. Use of PMOS keeper in domino CMOS
This problem will be more tactile for the
case when there is a large number of serially
connected NMOS transistors in the PDN. In this
case, discharging of CL will be very slow due to the
keeper contention current.
III.
Proposed Domino CMOS circuit
Our proposed technique to speed up the
discharging process of the dynamic-node capacitor.
The technique uses current mirror of suitable
mirroring ratio to achieve the motive and it results in
remarkable advances in reducing the time delay as
compared to other well known designs
The proposed circuit is designed for two input AND
gate with long chain of NMOS transistors and
current mirror draws the keeper contention current
and speeds up the discharging process.
IV.
Working of proposed circuit
The proposed circuit works in following
manner that during the precharge phase, Qewill be
deactivated, thus the current through the transistor,
M1 will be zero. By the effect of the current mirror
formed from M1 and M2, the current of M2 will also
be zero allowing CL to charge to VDD. During the
evaluation phase, the CLK signal will be at logic
"1", thus closing the path to ground. If the inputs
status is such that there is no current path through
the PDN, the current through M1 and M2 will
remain zero, thus leaving CL charged at VDD.
Fig 3 Proposed circuit having current mirror
Likewise, if the inputs status is such that
there is a current path through the PDN, the
relatively small current through M1 will be mirrored
through M2, thus speeding up the discharging
process of CL. Increasing the current-mirroring ratio
will speed up the discharging process further. The
speed improvement gained from this method
increases when the number of the series-connected
NMOS transistors increases. In case of noise
margin, the dynamic-node voltage, VCL will be
discharged not to 0 V; instead, it discharges to the
threshold voltage of the transistor, M1. So, the
threshold voltage of this transistor will be put equal
to 0 V. Even if there is an external noise on the gate
of this transistor, it will not conduct as the other
NMOS transistors of the chain are not conducting.
So for very long chain of series-connected NMOS
transistors in the PDN, the discharging current
through M1 will be relatively small and will
decrease with increasing the number of NMOS
transistors in the chain. In such circuits, to obtain a
significant increase in speed, the current mirroring
ratio, iM2/iM1= (W/L)2/(W/L)1 needs to be
increased to a large value, typically 20. Achieving
this relatively large current-mirroring ratio by the
conventional current mirror will result in an
increased capacitance at the gate terminal of M1 and
M2, thus slowing down the operation. Also,
increasing the current-mirroring ratio to such a large
value using the rudimental method causes the
dynamic-node capacitance, CL to increase, thus
degrading the speed further.
463 | P a g e
Lalit Mishra, Nitin Meena / International Journal of Engineering Research and Applications
(IJERA)
ISSN: 2248-9622
www.ijera.com
Vol. 3, Issue 4, Jul-Aug 2013, pp. 462-465
Fig 4 LAYOUT OF Proposed Cicuit
Fig 5 Voltagevs Time Analysis
V.
Conclusion
It will be found that the current mirroring
ratio, m of the current mirror must lie within a
certain range so that the discharging process will not
be adversely affected by the addition of the current
mirror. Domino circuits have offered an improved
performance in speed and power when compared
with CMOS circuit. This range will be determined
quantitatively. The simulation results for comparing
the conventional and proposed techniques for the
0.12 μm technology are presented. There are an
increasing number of applications that require the
use of a large number of NMOS transistors in series
in the pull-down network of the CMOS domino
logic.
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Lalit Mishra, Nitin Meena / International Journal of Engineering Research and Applications
(IJERA)
ISSN: 2248-9622
www.ijera.com
Vol. 3, Issue 4, Jul-Aug 2013, pp. 462-465
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